There are many industries that utilize conveyor belts to transport raw materials and components as well as finished goods during various manufacturing and handling processes. Often it is helpful to quantify by weight the materials conveyed on the belts.
Load sensing assemblies for measuring weight of loads on a conveyor must contend with both vertical and horizontal directional force components. Certain cantilevered parallel beam load cells are described by Kemp in U.S. Pat. No. 4,682,664, for example, connected to belt supports such as weigh idlers. These load cells are most commonly referred to in the trade as “Single Point” load cells. Other names include “Parallelogram” load cells, “Platform” load cells, “Cantilevered Dual Parallel Beam” load cells and “Cantilevered Triple Parallel Beam” load cells. Such load cells are available in a wide range of capacities starting as low as one or two kg for low-density loads, and generally exhibit exceptional insensitivity to moments created by “off-center” placement of loads. They also have high structural robustness to lateral forces, particularly if they are applied in the same direction as the direction of the cantilevered beams. The parallelogram structure created by at least two cantelevered parallel beams responds to deflection in a manner similar to that of a parallelogram linkage such that the load receiving column moves parallel to the support bearing column, thereby minimizing any tilting of the weigh idler in the direction of the movement of the belt.
Single point load cells when used to support a single, typically planar weigh platform or deck exhibit a high degree of insensitivity to the positioning of a vertical load anywhere upon it. However, if the weigh platform is coupled externally to any other structure which impedes the normal linear and angular deflections that would occur due to the moments generated by off-center loading, the effectiveness of the built-in compensation may be seriously compromised, especially when attempting to measure light loads. Rigidly securing the ends of a weigh idler shaft to two such load cells creates this particular problem. Additionally, horizontal forces, especially drag, produced by the moving belt over the weigh idler create moments about the shaft which likewise compromise the effectiveness of the built-in compensation.
A suspension-type strain gauge transducer structure for platform scales is disclosed by Laimins in U.S. Pat. No. 3,512,595. Wire-type coupling elements or box-beam members are disposed at one or more locations about the platform.
It is therefore desirable to have a load sensing system which is more sensitive to light loads on conveyor belts such as encountered in the snack food and cereal industries.